The present invention relates to an apparatus for cooling a high pressure, hot gas laden with ash particles, and more particularly to a heat exchanger design for recovering heat from the high temperature combustible product gas produced in a pressurized coal gasifier, and for utilizing the heat recovered from the gas to produce superheated steam.
A number of coal gasification schemes have been developed in the past few years which produce a combustible product gas which can be ungraded to pipeline quality to supplement our nation's natural gas resources. The chemical reactions occurring in these gasification processes typically occur at temperatures ranging from 2000.degree. to 3000.degree. F. Further, pressures in the range of 250 to 1500 psi are required in order to satisfy system requirements. Other gas cleaning and processing steps are required subsequent to the gasification reaction to produce a product gas suitable for pipeline transmission. Prior to these gas cleaning and processing steps, it is necessary to cool the product gas leaving the gasification chamber from a temperature as high as 3000.degree. F. to a much lower gas handling temperature typically on the order of 400.degree. to 600.degree. F.
A major problem associated with the cooling of the gas leaving the gasification chamber is the high concentration of molten ash in the product gas. Special precautions must be taken to avoid plugging of the heat exchanger with accumulated ash deposits which would adversely affect heat transfer and pressure drop through the heat exchange section.
An additional problem associated with cooling the product gas in a pressurized gasifier is that the reduced gas volume associated with the high gas pressures results in extremely high ash loadings. Typical ash loadings encountered in pressurized gasifier heat exchange sections exceed 500 pounds ash per hour per foot squared of flow area as compared to typical ash loadings of 10 to 50 pounds ash per hour per square foot of flow area in conventional coal fired power plant heat exchanger surface.